1. Field of Invention
The present disclosure of invention relates to thin-film transistor (TFT) substrates of the type used in flat panel displays and to methods of fabricating the same, and more particularly, to a TFT array substrate whose array of transistors exhibit a high charge mobility and a high on/off current ratio and a method of fabricating the same.
2. Description of Related Technology
As liquid crystal displays (LCDs) become larger in size and higher in image resolution or other qualities, it becomes desirable to enhance electrical characteristics of thin-film transistors (TFTs) that are integrally formed in LCD panels, where the TFT's act as switches that couple image signals to pixel units containing the liquid crystals. In conventional TFTs, a hydrogenated form of amorphous silicon (a-Si:H) is used as a semiconductor film within which a channel portion of each TFT is formed.
The hydrogenated amorphous silicon, however, has a relatively low charge mobility and on/off current ratio as compared to field effect transistors (MOSFETs) whose channels are formed of monocrystalline silicon. In addition, since the hydrogenated amorphous silicon has an energy band gap of approximately 1.8 eV, it can convert light produced by an LCD backlighting unit into an undesirable leakage photocurrent that distorts the desired liquid crystal state for a given image. Also, an undesirable afterimage can be created due to an increase over time in the number of dangling bonds present in the a-Si:H TFT structure. Consequently, the already poor characteristics of the a-Si:H TFTs deteriorate over time as more dangling bonds are created.